The present invention relates generally to buffing large metal skins having different three-dimensional shapes, and more particularly to a buffing fixture and structure for supporting the exterior metal skins of airplanes during a buffing operation.
The exterior surface of an airplane is generally comprised of a plurality of large metal sheets, which are referred to as "skins". Previously, it has been a common practice to paint most or all of the exterior surface of the airplane to protect the surface of the skins. Recently, there has been a move to substitute for the use of paint on the skins highly polished metallic or "bright" surfaces. By providing bright surfaces, the airplane eliminates the weight of the paint and any drag caused by the paint. Additionally, the bright surfaces or highly polished exterior skins also provide a desirable cosmetic appearance for the airplane.
Each of the airplane skins are generally comprised of a very large and thin sheet of metal, such as steel or aluminum. Additionally, these skins will be fabricated in various sizes, shapes and contours. For example, the three-dimensional characteristics of a skin near the nose of the airplane will be considerably different than the three-dimensional characteristics of a skin used for the mid-section of the airplane. Accordingly, it should be appreciated that the large size, thinness and varying shapes of the airplane skins combine to make the task of buffing a set of airplane skins a formidable problem. For example, substantial pressure must be applied to the skins by a rotating buffing head in order to adequately polish the surface of the skins. However, due the fact that airplane skins are relatively thin, extreme care must be exercised to avoid damaging thereto. The problem may be analogized to buffing a sheet of foil. In other words, the buffing process could cause undesirable deformities or distortions in the shape of the skins.
Additionally, it would be desirable if the process of buffing a set of airplane skins could be automated in order to permit the airplane to be built as quickly and as cost efficiently as possible. However, the process would have to be capable of being adapted to the varying shapes of the skins, and a way of preventing the deformation of the skins would have to be developed.
Accordingly, it is a principal objective of the present invention to provide a buffing fixture and structure for supporting relatively large and thin metal sheets having various shapes, such as a set of skins for an airplane.
It is another objective of the present invention to provide a buffing fixture which will prevent any significant distortion or deformation of the skins as a result of an automated buffing process.
It is an additional objective of the present invention to provide a support structure which will permit a plurality of skins to be finished simultaneously.
It is yet another objective of the present invention to provide a support structure and method which will permit the use of one or more robots to buff the one or more skins while additional skins are being mounted to the same apparatus.
It is a further objective of the present invention to provide a support structure which will permit an exceptionally large skin to be buffed or otherwise finished across multiple support structures.
To achieve the foregoing objectives, the present invention provides a universal buffing fixture and structure for supporting large and thin metal skins during a finishing operation, which includes: a plurality of individual form fixtures, at least one trunnion table mounted for rotation along a horizontally disposed axis, and a motor for causing the rotation of the trunnion table. Each of the form fixtures is comprised of a frame having at least one brace which extends outwardly from the frame, a form shell mounted to the frame such that the interior surface is in contact with a longitudinal edge of the brace, and a layer of foam disposed substantially along the entire interior surface of the form shell in order to support the surface area of the form shell. The form shell has a three dimensional shape which follows the three dimensional shape of the metal skin to be finished. A set of straps are also provided in order to removably secure the metal skin to the form shell, such that the metal skin lies flush against the exterior surface of the form shell.
In one embodiment according to the present invention, a pair of trunnion tables are provided being positioned to enable exceptionally large metal skins to be supported across both tables. In this regard, the trunnion tables are mounted for rotation along a common horizontal axis, and a pair of servo motors are provided to cause a synchronous rotation of the trunnion tables.
One advantage of the present invention is that the buffing fixture and structure permit the use of one or more robots to finish a plurality of skins supported on the trunnion tables. Another advantage of the present invention is that the trunnion tables may incorporate a second form fixture thereon to allow at least one metal skin supported on one side of the table to be subjected to a buffing operation, while a second metal skin is being mounted to the other side of the trunnion table. Still another advantage of the present invention is that the structure permits a single buffing head per robot to finish the entire skin. A further advantage of the present invention is that the buffing fixture may be repeatedly used to support metal skins having the same shape, thereby insuring greater uniformity among finished skins as well as reducing the likelihood that any metal skin could be deformed during the buffing process due to the pressure exerted upon the skin by the buffing head.
Other objectives, features and advantages of the present invention will be readily appreciated and better understood by referring to the following description and accompanying drawings.